Much work had been done to date on amylin, calcitonin, and calcitonin gene related peptide (CGRP) to understand their structure and function. Table 1 provides a summary of some biological effects of CGRP, calcitonin and amylin as published in Wimalawansa, S. J. (1997) Critical Reviews in Neurobiology, 11; 167-239.
TABLE 1Biological effectCGRPCalcitoninAmylinVasodilation+++++/−++Chronotropic++−++Inotropic++−++Inhibit bone resorption+++++++Stimulate bone formation−−+Calcium-lowering effect−+++++Growth factor-like effect+−+Neural regeneration+++/−−Thermoregulation+−+Inflammation+++/−−Gastric mucosal protection++−−Effects on β cells++/−++Skeletal muscle+−+Glucose metabolism+−+Anorectic effect+++++Analgesic effect−+++
Amylin has been reported to regulate gastric emptying and suppress glucagon secretion and food intake, thus regulating the rate of glucose appearance in the circulation. It appears to complement the actions of insulin, which regulates the rate of glucose disappearance from the circulation and its uptake by peripheral tissues. These actions are supported by experimental findings in rodents and humans, which indicate that amylin complements the effects of insulin in postprandial glucose control by at least three independent mechanisms, all of which affect the rate of glucose appearance. First, amylin suppresses postprandial glucagon secretion. Compared to healthy adults, patients with type 1 diabetes have no circulating amylin and patients with type 2 diabetes have diminished postprandial amylin concentrations. Furthermore, infusion of an amylin specific monoclonal antibody, which bound circulating amylin, again resulted in greatly elevated glucagon concentrations relative to controls. Both of these results point to a physiological role of endogenous amylin in the regulation of postprandial glucagon secretion. Second, amylin slows gastrointestinal motility and gastric emptying. Finally, intrahypothalamic injections of rat amylin were shown to reduce feeding in rats and alter neurotransmitter metabolism in the hypothalamus. In certain studies, food intake was significantly reduced for up to eight hours following the intrahypothalamic injection of rat amylin and rat CGRP. In human trials, an amylin analog, pramlintide, has been shown to reduce weight or weight gain. Amylin may be beneficial in treating metabolic conditions such as diabetes and obesity. Amylin may also be used to treat pain, bone disorders, gastritis, to modulate lipids, in particular triglycerides, or to affect body composition such as the preferential loss of fat and sparing of lean tissue.
The hormone calcitonin (CT) was named for its secretion in response to induced hypercalcemia and its rapid hypocalcemic effect. It is produced in and secreted from neuroendocrine cells in the thyroid that have since been termed C cells. The best-studied action of CT(1-32) is its effect on the osteoclast. In vitro effects of CT include the rapid loss of ruffled borders and decreased release of lysosomal enzymes. Ultimately, the inhibition of osteoclast functions by CT results in a decrease in bone resorption. However, neither a chronic reduction of serum CT in the case of thyroidectomy nor the increased serum CT found in medullary thyroid cancer appears to be associated with changes in serum calcium or bone mass. It is thus most likely that a major function of CT(1-32) is to combat acute hypercalcemia in emergency situations and/or protect the skeleton during periods of “calcium stress” such as growth, pregnancy, and lactation. (Reviewed in Becker, JCEM, 89(4): 1512-1525 (2004) and Sexton, Current Medicinal Chemistry 6: 1067-1093 (1999)). Consistent with this is recent data from the calcitonin gene knockout mouse, which removes both the calcitonin and the CGRP-I peptides, that revealed that the mouse had normal levels of basal calcium-related values, but an increased calcemic response (Kurihara H, et al, Hypertens Res. 2003 February; 26 Suppl:S 105-8).
CT has an effect on plasma calcium levels and inhibits osteoclast function and is widely used for the treatment of osteoporosis. Therapeutically, salmon CT appears to increase bone density and decrease fracture rates with minimal adverse effects. CT has also been successfully used over the past 25 years as a therapy for Paget's disease of bone, which is a chronic skeletal disorder that may result in enlarged or deformed bones in one or more regions of the skeleton. CT is also widely used for its analgesic effect on bone pain experienced during osteoporosis, although the mechanism for this effect is not clearly understood.
Calcitonin gene related peptide (CGRP) is a neuropeptide whose receptors are widely distributed in the body, including the nervous system and the cardiovascular system. This peptide seems to modulate sensory neurotransmission and is one of the most potent endogenous vasodilatory peptide discovered to date. Reported biological effects for CGRP include: modulation of substance P in inflammation, nicotinic receptor activity at the neuromuscular junction, stimulation of pancreatic enzyme secretion, a reduction of gastric acid secretion, peripheral vasodilation, cardiac acceleration, neuro-modulation, regulation of calcium metabolism, osteogenic stimulation, insulin secretion, an increase in body temperature and a decrease in food intake. (Wimalawansa, Amylin, calcitonin gene-related peptide, calcitonin and ADM: a peptide superfamily. Crit Rev Neurobiol. 1997; 11(2-3): 167-239). An important role of CGRP is to control blood flow to various organs by its potent vasodilatory actions, as evidenced by a decrease of mean arterial pressure following intravenous administration of CGRP. The vasodilatory actions are also supported by recent analysis of homozygous knockout CGRP mice, which demonstrated elevated peripheral vascular resistance and high blood pressure caused by increased peripheral sympathetic activity (Kurihara H, et al, Targeted disruption of ADM and alphaCGRP genes reveals their distinct biological roles. Hypertens Res. 2003 February; 26 SuppliS105-8). Thus, CGRP appears to elicit vasodilatory effects, hypotensive effects and an increase in heart rate among other actions.
Prolonged infusion of CGRP into patients with congestive cardiac failure has shown a sustained beneficial effect on hemodynamic functions without adverse effects, suggesting a use in heart failure. Other indications of CGRP use include renal failure, acute and chronic coronary artery ischemia, treatment of cardiac arrhythmia, other peripheral vascular disease such as Raynaud's phenomenon, subarachnoid hemorrhage, hypertension, and pulmonary hypertension. Preeclamptic toxemia of pregnancy and preterm labor is also potentially treatable. (Wimalawansa, 1997). Recent therapeutic uses include the use of CGRP antagonists for the treatment of migraine headaches.
There are many beneficial properties of each peptide that can be used alone or in combination to treat or prevent a variety of conditions. It would be useful to create new and useful peptides having multiple actions that impart improved characteristics not possessed by the existing peptides. For example, in food intake assays, amylin has been shown to have a quick onset, within 30 minutes, but its effect tapers off after 60 minutes. In contrast, salmon calcitonin has been shown to have a delayed effect, with peak levels still maintained at 240 minutes. Novel compounds that can mimic the effects of amylin and/or calcitonin and have quick onset of activity like amylin with the sustained activity of calcitonin may increase the potency and efficacy of either compound alone. Moreover, the combination of certain physicochemical characteristics of amylin, calcitonin, and/or CGRP into a single modality may facilitate intervention at different points in a dysfunctional metabolic circuit. These novel compounds combine desirable activities or properties for a superior therapeutic, which may result in compounds having at least one desirable characteristic such as higher efficacy, greater potency, greater bioavailability, fewer side effects, ease in manufacture, stability, and/or solubility.
All documents referred to herein are incorporated by reference into the present application as though fully set forth herein.